Hydrocarbons, such as oil and gas, are commonly obtained from subterranean formations that may be located onshore or offshore. The development of subterranean operations and the processes involved in removing hydrocarbons from a subterranean formation typically include a number of different steps such as, for example, drilling a wellbore at a desired well site, treating the wellbore to optimize production of hydrocarbons, and performing the necessary steps to produce and process the hydrocarbons from the subterranean formation.
Downhole tools and completion strings may use isolation devices and/or pressure barriers such as packers and others for isolating one zone from another or for isolating a plurality of zones. Some isolation tools are designed to maintain a pressure differential in one direction only, which may be referred to as unidirectional pressure barrier tools and/or unidirectional isolation tools. Other isolation tools are designed to maintain a pressure differential in both directions, which may be referred to as dual directional pressure barrier tools and/or dual directional isolation tools. Pressure on seals may be exerted by reservoir pressures, by pressure applied from the surface into an annulus, and by other pressure sources. Pressure may be exerted by liquids and/or gases. Some isolation devices and/or pressure barrier tools are designed to be deployed, to seal, to unseal, and to be retrieved from the wellbore, which may be referred to as retrievable tools.
Isolation devices may be used when it is desired to pump cement or other slurry down the tubing and force the cement or slurry around the annulus of the tubing or out into a formation. It then becomes necessary to seal the tubing with respect to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well or for otherwise isolating specific zones in which a well bore has been placed. Downhole tools referred to as packers and bridge plugs are designed for these general purposes and are well known in the art of producing oil and gas.
Since downhole conditions can be extreme, certain packers need to be able to withstand the stresses induced by relatively high differential pressures and high temperatures found within such wellbore environments. The assignee of the present disclosure discovered that when using larger packer type tools, or when using packer type tools in higher temperature and/or higher differential pressure environments, such as those having nominal diameters exceeding six (6) inches, temperatures exceeding 250° F., or differential pressures exceeding 10,000 psi, there was a possibility for the segmented packer element back-up shoes, also referred to as back-up rings, to allow the packer element to extrude through gaps that are formed between the packer OD and the tubing or casing ID when the packer element was activated. Upon certain conditions, the larger OD packer elements, and smaller OD packer elements upon being subjected to elevated pressures and temperatures, were subject to being extruded through these gaps thereby possibly damaging the packer element and possibly jeopardizing the integrity of the seal between the wellbore and the packer element. Also, in the high expansion field, the risk of unwanted extrusion is even higher. This is where the back-up rings are not able to provide much resistance to extrusion of the elastomeric element between the large gap formed between the OD of the packer and the tubing or casing ID given the substantial differences in these diameters in such applications.
Thus, there remains a need in the art for packers having back-up elements that prohibit, or at least significantly reduce, unwanted extrusion of packer elements into the annulus formed between the tubing string and wellbore.